In the arc welding process the welder must view his work while an arc is being drawn through a tinted lens window in his helmet. This is to protect his eyes from the brightness of the arc. Tinted windows provided for this purpose are so dark that it is not possible to satisfactorilly view work through such windows when the arc is not struck. This necessitates alternate means for viewing the work prior to creation of an arc.
Typically, with single window helmets, the welder may remove or tilt back the entire helmet in order to view his work. This occupies time and may require the use of one hand.
Arrangements have been built into welding helmets to provide for the temporary opening of the tinted window either by sliding or hinged mechanisms. Such mechanisms have been operated by hand, by movement of the chin or by pressure from the welder's breath. These mechanisms are not entirely convenient to use.
It has also been proposed to provide a welding helmet with two adjacent viewing windows one with a tinted lens and one with a clear lens. For example, U.S. Pat. No. 2,362,637 to W. L. Keehn discloses two such vertically aligned window lens elements set in place of the customary single lens window of a typical helmet. To view alternately through the respective window lenses, the user of this apparatus need only tilt his head upwardly, carrying the helmet with his head, so as to align the desired window with the workpiece. To ensure that excessive light does not enter the mask through the clear lens while welding is in progress, this helmet carries an outwardly protruding visor, fixed along the line where the upper tinted lens and lower clear lens meet. While welding, this visor ensures that the lower, clear lens is shadowed from the brightness of the arc.
In another U.S. Pat. No. 2,644,160 to J. H. Jacobs, a similar arrangement is adopted, except that the clear lens is mounted above and rearwardly from the tinted lens. According to this patent, the user must tilt his head downwardly, in order to view his work through the clear window. By offsetting the clear lens rearwardly of the tinted lens, this helmet relies on the frame around the tinted lens to serve the function of the visor in the Keehn patent.
Both of these prior art patents rely upon opaque visor-like surfaces to shadow the clear lens window of the mark from the brightness of the art. The presence of a visor intermediate the viewing lines between the respective windows forces the user to tilt his head to a greater degree when switching his view between such windows. Thus the fields of view through such windows are not virtually contiguous. Additionally, the field of view, in both cases, is limited by the presence of the visor element.
Furthermore, in both such masks the lenses are mounted relatively close to the user's face and are therefore liable to collect condensation arising from moisture present due to sweat or exhaled breath. This can obscure vision and create discomfort.